RU2186830C2 - Method of increasing quality of sulfur-containing fraction of raw material (versions) - Google Patents

Abstract

FIELD: petrochemical processes. SUBSTANCE: low-sulfur gasoline is obtained from olefin sulfur-containing cracking ligroin (naphtha) by treatment with acid catalyst, preferably zeolite with middle pore size such as ZSM-5 for cracking of low-octane paraffins and olefins under rather mild conditions at limited aromatization of olefins and naphthenes. The following step is hydrodesulfurization catalyzed by hydrofining catalyst such as CoMo/alumina. In the first treatment stage involving acid catalyst, olefins, which would be saturated in the hydrodesulfurization stage to lower octane number of product, are converted into compounds favorably contributing to anti-knock properties of products. Total yield of liquid products us high, commonly at least 90%. Level of aromatic hydrocarbons in products increases generally no more than by 25% and can even be lower than in raw material. EFFECT: reduced sulfur level to acceptable value at no loss in octane number. 10 cl, 3 tbl, 4 ex

Description

FIELD OF THE INVENTION
The present invention relates to a method for improving the quality of hydrocarbons. More specifically, it relates to a method for improving the quality of petroleum fractions with boiling ranges of gasoline containing significant proportions of benzene and sulfur impurities, while minimizing the octane losses that occur after sulfur removal by hydrogenation.

State of the art
Catalytic cracked gasoline makes up the bulk of gasoline products in the United States. When the cracked feed contains sulfur, naphtha cracked products usually contain sulfur impurities, which usually need to be removed usually by hydrotreating in order to bring them into line with the standard standards for the product in question. It is assumed that in the future these standard norms will become more stringent, allowing no more than 300 masses. ppm sulfur (or even lower) in gasoline and other fuels. Despite the fact that the sulfur content in the product can be reduced by hydrodesulfurization of naphtha cracking, the process is expensive both from the point of view of capital construction and from the point of view of operating costs, since significant amounts of hydrogen are consumed.

 As an alternative to desulphurization of the cracked feed, products that need to be brought into line with standard low sulfur standards can be hydrotreated, usually using a catalyst containing a Group VIII or VI element of a periodic system of elements such as cobalt or molybdenum, or individually or in combination with each other, on an appropriate carrier, such as alumina. In the hydrotreatment process, molecules containing sulfur atoms are mildly hydrocracked to convert sulfur to an inorganic form, hydrogen sulfide, which can be removed from the liquid hydrocarbon product in a separator. Although this hydrotreating method is an efficient process that has been put into practice for many years for gasoline and heavier oil fractions in order to obtain satisfactory products, it has disadvantages.

 Cracked naphtha (naphtha) originating from a catalytic cracking unit and without any further processing, such as purification operations, has a relatively high octane number due to the presence of olefin components, and essentially cracked gasoline is an excellent contributor to the gasoline octane range. It contributes to the production of a large quantity of product with a high octane mixing ratio. In some cases, this fraction can produce up to half of gasoline in the aggregate of refinery products.

 Other highly unsaturated fractions boiling within the boiling range of gasoline, which are obtained at some refineries or petrochemical plants, include pyrolysis gasoline, obtained as a by-product from the cracking of oil fractions to form light olefins, mainly ethylene and propylene.

 Pyrolysis gasoline has a very high octane number, but is completely unstable in the absence of hydrotreating, since, in addition, the desired olefins boiling within the boiling range of gasoline also contain a significant proportion of diolefins, which tend to form resins during storage.

 Hydrotreating these sulfur-containing cracked naphtha fractions, as a rule, causes a decrease in the olefin content and, consequently, a decrease in the octane number; when the degree of desulfurization increases, the octane number of the product with the boiling range of gasoline decreases. A certain amount of hydrogen can also cause hydrocracking to some extent, as well as olefin saturation, depending on the conditions of the hydrotreating operation.

 Various proposals have been put forward for the removal of sulfur while preserving olefins, which make a positive contribution to the octane number. Sulfur impurities tend to be concentrated in the heavy gasoline fraction, as noted in US Pat. No. 3,957,625 (Orkin), which proposes a method for removing sulfur by hydrodesulfurization of a heavy fraction obtained by catalytic cracking of gasoline in order to preserve the octane contribution from olefins, which are mainly in the lighter fraction. According to one type of conventional commercial operation, the heavy gasoline fraction is purified in this way. Alternatively, the hydrodesulfurization selectivity relative to olefin saturation can be changed by selecting a suitable catalyst, for example, by using magnesium oxide as a carrier instead of the more common alumina. US Pat. No. 4,049,542 (Gibson) proposes a process in which a copper catalyst is used to desulphurize an olefinic hydrocarbon feed, as well as obtained by catalytic cracking of light naphtha.

 In any case, not paying attention to the mechanism by which this occurs, the decrease in the octane number, which takes place as a result of sulfur removal by hydrotreating, causes a dissonance between the increasing need to produce gasoline with a higher octane number and the need to obtain completely combustible, less polluted low-sulfur fuels. This inherent dissonance is even more noticeable in the current situation with low-sulfur oils.

 Other purification methods for catalytic cracked gasolines have also been proposed in the past. For example, U.S. Pat. fraction. Another method in which cracked gasoline is separated prior to refining is described in US Pat.

In US patent 5143596 (Maxwell) and European patent EP 420326-B1 describes methods for refining sulfur-containing feedstock in the field of gasoline by reforming using a sulfur-resistant catalyst that is selective for aromatization. Catalysts of this kind include metal-containing crystalline silicates, including zeolites, such as gallium-containing ZSM-5. The process described in US Pat. No. 5,143,596 relates to hydrotreating an aromatic effluent from a reforming step. Conversion of naphthenes and olefins to aromatics is at least 50% in severe conditions used, typically temperatures of at least 400 ^o C ^(about 750 F) and usually higher, e.g., at 500 ^o C ^(about 930 F). Under such conditions, conventional reforming is typically accompanied by significant and undesirable yield losses, usually more than 25%, and the same is true for the methods described in these publications: C ₅₊ yields in the range of 50-85% are reported in European Patent 420326. the method, therefore, has a traditional disadvantage of reforming, so that the problem of developing a method in which it is possible to reduce the sulfur content in cracking naphtha while minimizing yield losses, as well as reducing hydrogen consumption, remains in the same state.

 US Pat. No. 5,346,609 describes a method for reducing the sulfur content of cracked naphtha, first by hydrotreating the naphtha to convert sulfur to an inorganic form, then by treating it with a catalyst such as ZSM-5 to recover the octane loss during the hydrotreating step, mainly by selective cracking of low octane paraffins. This method, which is commercially successful, leads to a low-sulfur naphtha with a good yield, which can be directly introduced into the gasoline collection.

SUMMARY OF THE INVENTION
Currently, the authors have developed a method for catalytically desulfurizing cracked fractions with gasoline boiling limits, which allows reducing the sulfur content to acceptable levels essentially without decreasing the octane number. The usefulness of this method is to reduce the consumption of hydrogen and to reduce the formation of mercaptans, compared with the method described in US patent 5346609, and to obtain higher yields than achieved by reforming, including methods such as described in US patent 5143590 and application for European patent EP 420326 B1.

According to the present invention, a method for improving the quality of cracked naphtha includes the first stage of catalytic treatment, in which selective cracking of low-octane paraffins and olefins occurs under mild conditions, so that the aromatization of olefins and naphthenes in the feed is kept at a low level, usually not more than 25 wt.% . The hydrotreating stage, which follows the catalytic treatment stage, leads to a decrease in sulfur content and is less harmful to the octane number due to the removal of olefins during the first stage, and as a result, the octane number of the product is close to or even exceeds that of the original naphtha feed. The total yield of liquid products (C ₅₊ ) is high, usually amounting to at least 90 wt.%, Due to the mild conditions used in the first stage of the method, and the degree of aromatization is limited. By converting the cracking naphtha to the hydrotreatment stage, olefin saturation and hydrogen consumption are reduced. Also, by performing the last hydrodesulfurization, the formation of mercaptans is eliminated due to the combination of hydrogen sulfide with an olefin using a zeolite catalyst, which potentially leads to a higher degree of desulfurization or to reduce the need for processing of a further product, for example, as described in US patent application 08/001681.

 The method can be used to desulphurize light and wide ligroin fractions while maintaining the octane number so as to eliminate the need for reforming of such fractions or at least without the need for reforming such fractions to a previously considered necessary degree.

 In practice, it may be desirable to hydrotreat the cracked ligroin before it is brought into contact with the catalyst in the first aromatization / cracking step in order to reduce the diene content of the ligroin and thus increase the catalyst life. Only a very limited degree of saturation of the olefin is achieved in the pre-cleaner and only a small amount is subjected to desulfurization during this time.

Feedstock
The feedstock for the method includes a sulfur-containing oil fraction, which boils within the boiling range of gasoline. Raw materials of this type typically include light naphtha, typically having a boiling range of C ₆ to 166 ^o C ⁽³³⁰ ° F), a broad naphtha, typically having a boiling range from C ₅ to 216 ^o C (420 ^to F), heavier naphtha fractions boiling in the range 127-211 ^o C (260-412 ^about F), or heavy gasoline fractions boiling out, or at least boiling out, in the range 166-211 ^o C (330-500 ^about F), preferably 166-260 ^o C (330-412 ^o F). In many cases the feedstock is 95% temperature (determined according to ASTM D 86) of at least 163 ^o C (325 ^to F) and preferably at least 177 ^o C (350 ^o F), e.g., 95% the temperature is at least 193 ^o C (380 ^o F) or at least 220 ^o C (400 ^o F).

 Catalytic cracking is a suitable source of cracking naphtha, usually fluid catalytic, but thermal cracking methods, such as coking, can also be used to produce usable raw materials such as ligroin, pyrolysis gasoline, and others from the process. thermal cracking ligroins.

The method can be carried out using a pure ligroin fraction obtained from the catalytic or thermal cracking step, or, alternatively, a part thereof. Since sulfur tends to concentrate in higher boiling fractions, it is preferable, especially when the plant capacity is limited, higher boiling fractions are separated and subjected to the steps of the present process without treating the lower boiling fraction. Boundaries boiling between treated and untreated fractions may vary according to the presence of sulfur compounds, but typically suitable boundary boiling fractions in the range of from 38 ^o C (100 ^o F) to 150 ^o C (300 ^o F), more usually in the range of 93 ° ^{C (200 °} F) to 150 ^o C (300 ^o F). The exact choice of the boiling range of the fractions depends on the standard norms for sulfur for gasoline, as well as on the type of sulfur compounds present: lower boiling ranges are usually necessary in the case of standard norms for a lower sulfur content in the product. Sulfur which is present in components boiling below 65 ^o C ^{(150 °} F), typically in the form of mercaptans which may be removed by treatment with an extractive type, such as a treatment by Merox but hydrotreating is appropriate for the removal of thiophene and other cyclic sulfur compounds present in higher boiling components, for example, in fractions of components boiling above 82 ^o C (180 ^o F). Processing a lower boiling fraction in an extractive type process combined with hydrotreating higher boiling components can therefore be an economically preferred process parameter. Broader boiling ranges of the fractions are preferable to minimize the amount of feed that passes through the hydrotreatment unit, and ultimately select the boiling ranges of the fractions along with other process parameters, such as the type of extraction, therefore, desulfurization is carried out in accordance with standard product standards, feedstock limitations and other factors.

The sulfur content in the cracked fraction depends on the sulfur content in the cracking feedstock, as well as the boiling range of the selected fraction used as feedstock in the method. Lighter fractions, for example, tend to have lower sulfur contents than higher boiling fractions. Almost sulfur content exceeds 50 mass. ppm and usually is more than 100 mass. ppm, and in most cases more than 500 mass. ppm For the fractions which have 95% to temperatures above ^about 193 C ⁽³⁸⁰ F), the sulfur content may exceed 1000 mass. ppm and can be as high as 4000 or 5000 mass. ppm or even higher as shown below. The nitrogen content is not a characteristic of the raw material, as the sulfur content, and is preferably not more than 20 mass. ppm, although higher amounts of nitrogen, usually up to 50 mass. h / million, can be found in certain higher boiling feedstock with 95% temperatures above ^about 193 C ⁽³⁸⁰ F). The nitrogen content, however, is usually not higher than 250 or 300 mass. ppm As a result of the cracking that precedes the steps of the present process, the feed for the hydrodesulfurization step is olefinic with an olefin content of at least 5 mass. % and more typically in the range of 10-20 wt.%, for example, 15-20 mass. %; preferably, the feed contains olefins in an amount of 10-20 wt.%, sulfur in an amount of 100-5000 wt. ppm, nitrogen in an amount of 5-250 mass. ppm and benzene at least in the amount of 5 vol.%. Thermal cracking ligroins often contain dienes, however, as described below, they are preferably removed by hydrogenation as a pre-treatment step.

Method configuration
The selected sulfur-containing feedstock with boiling range of gasoline is processed in two stages by first passing ligroin through a selective acid catalyst to selectively crack low octane paraffins and converting some of the olefins and naphthenes into aromatic hydrocarbons and aromatic side chains by alkylating aromatic hydrocarbons originally present in the raw materials or formed due to the conversion of olefins. The effluent from this stage then enters the hydrotreating stage, in which the sulfur compounds present in the ligroin feedstock, which are mostly unconverted in the first stage, are converted into an inorganic form (H ₂ S), which can be removed in a separator following hydrodesulfurization. Since in the first stage (cracking / aromatization) no products are obtained that interfere with the operation of the second stage, the effluent of the first stage can be directly sent to the second stage without the need for separation between the stages,
In the first step of the process, the ligroin feed is first treated by contacting with an acid catalyst under conditions resulting in some aromatization of the olefins that are in the feed, due to cracking along with the selective cracking of low octane paraffins and olefins. Since olefins readily form aromatic hydrocarbons in the presence of selective catalysts, the conditions in this step are relatively mild and yield losses are low. The degree of aromatization is limited, and the content of aromatic hydrocarbons in the effluent of the first stage is comparable to that of the raw material. In both stages of the process, aromatization is below 50 wt.% (Conversion of olefins and naphthenes to aromatic hydrocarbons). The conversion of olefins and naphthenes to aromatic hydrocarbons is typically lower than 25 wt.% And often lower, for example, not more than 10 or 15 wt.%.

At low temperatures of the first stage, when the general chemistry of the method prevails, due to hydrotreating carried out in the second stage, the final product may contain less aromatic hydrocarbons than raw materials, due to the saturation of aromatic hydrocarbons using a hydrotreating catalyst. Mild conditions associated with a low degree of aromatization lead to a high yield of liquid products (C ₅₊ ), usually at least 90 vol. % or higher, for example, 95 vol. % or higher. In some cases, the yield of C ₅₊ may be higher than 100 vol. % as a result of low aromatization associated with volume expansion during hydrotreatment.

 The particle size and nature of the catalysts used in both stages are usually determined by the type of process used, such as: a liquid phase process with a fixed catalyst bed and a downward flow of feed; a method with a flowing thin stream of phase with a fixed catalyst bed and an upward flow of raw materials; a fluidized bed bubbler method; or a transport method with a fluidized bed of catalyst. All of these various process schemes are possible that are well known, although a fixed catalyst bed and a downward flow of feed is preferred because of its ease of use.

First stage processing
Compositionally, the first processing step is the selective cracking of low-octane feed components associated with a limited degree of aromatization of naphthenes and olefins to form aromatic hydrocarbons and aromatic side chains by alkylation of aromatic hydrocarbons. Olefins come from raw materials, as well as from an increasing amount of paraffins and olefins when cracking combined feeds. Some isomerization of n-paraffins into branched chain paraffins with an increase in the octane number may occur, which further contributes to the octane number of the final product. The conditions used in this step of the process are those which result in a controlled degree of selective cracking of low octane paraffins, mainly n-paraffins, naphtha feedstocks, along with the conversion of feed olefins and cracking of paraffins to form aromatic hydrocarbons and alkylate aromatic hydrocarbons with olefins. Typically, the first stage temperature is 150-455 ^{° C (about} 300-850 F), preferably 177-425 ^{° C (about} 350-800 F). The pressure in this reaction zone is not critical since hydrogenation does not occur, although lower pressure in this stage favors the favorable formation of olefins by cracking paraffins. The pressure, therefore, depends mainly on the suitability for the implementation of this stage. It is usually 445-10445 kPa (50-1500 psi), preferably 2170-7000 kPa (300-1000 psi), at hourly volumetric flow rates of the liquid, usually 0.5-10 (hour ^-1 ), usually 1-6 ( hour ^-1 ). The ratio of hydrogen to hydrocarbon feed is typically 0-890 L / L (under normal conditions) [0-5000 standard cubic feet per barrel], preferably 18-445 L / L (under normal conditions) [100-2500 standard cubic feet per barrel ] to minimize catalyst aging.

In the first stage, usually there is a change in the volume of material with the boiling range of gasoline. A slight decrease in the volume of the liquid product occurs as a result of the conversion to lower boiling products (C _5– ), however, the conversion to C _5– products is typically not more than 10 vol. %, and usually below 5 vol. % A slight decrease in the volume of liquid products usually occurs due to the conversion of olefins to aromatic hydrocarbons or their incorporation into aromatic hydrocarbons, however, due to the limited degree of aromatization under mild reaction conditions, it is typically no more than 5%. If the feedstock contains significant amounts of higher boiling components, the C content _5- products may be relatively lower and for this reason the use of the higher boiling naphthas is advantageous, especially the fractions with 95% temperatures above 177 ^{° C (350 °} F) and even more preferably greater than ^about 193 C ⁽³⁸⁰ F) or, for example, above 205 ^{° C} (400 ^° F). Typically, however, 95% of the temperature does not exceed ^about 270 C ⁽⁵²⁰ F), and typically not higher than 260 ^o C (500 ^o F).

 The catalyst used in the first step of the process has sufficient acid functionality to carry out the desired cracking, aromatization, and alkylation reactions. For this purpose, it has a significant degree of acid activity, and for this purpose, the most preferred materials are solid, crystalline, catalytic materials such as molecular sieves, these solid materials having an average pore size and the topology of a material acting as a zeolite, which, in aluminosilicate form, has permeability index 2-12. Preferred catalysts for this purpose are catalytic materials behaving as medium pore zeolites, for example, acidic materials having a top pore aluminosilicate zeolite topology. These zeolite catalyst materials are, for example, those which, in their aluminosilicate form, have a permeability index of 2-12. Reference should be made to US Pat. No. 4,784,745 with respect to determining a permeability index and describing a method for measuring this value, as well as the usefulness of the detailed information provided for a number of catalytic materials having the appropriate topology and structure of the pore system.

 Preferred medium pore aluminosilicate zeolites are those having the topology SZM-5, ZSM-11, ZSM-12, ZSM-21, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50 or MSM -22, MCM-36, MCM-49 and MCM-56, preferably in aluminosilicate form. (Modern catalytic materials identified by MSM numbers are disclosed in the following patents: MSM-22 zeolite is described in US Pat. No. 4,954,325; MSM-36 zeolite is described in US Pat. 56 is described in US Pat. No. 5,362,697). However, other catalytic materials having appropriate acid functionality may be used. A particular class of catalytic materials that can be used are, for example, large pore zeolites that have a permeability index of up to 2 (in aluminosilicate form). Zeolites of this type include mordenite, beta zeolite, fayazit, as well as zeolite Y and ZSM-4. Other refractory solid materials having the desired acid activity, pore structure and topology may also be used.

The catalyst should have sufficient acid activity to convert the corresponding components of the ligroin feed as described above. The only measure of the acid activity of a catalyst is its alpha number. An alpha test is described in US Pat. No. 335,408 and J. Catalysis, 4, 527 (19655; 6, 278 (1966); and 61, 395 (1980), all of which are referenced to describe this test. Experimental Test Conditions Used for determining alpha values given in this specification include a constant temperature of 538 ^C. and a variable flow rate as described in detail in J. Catalysis, 61, 395 (1980). the catalyst used in this step of the process suitably has an alpha activity of at least 20, usually in the range of 20-800 and preferably at least 50-200. alizatora not need a very high acid activity, since it is desirable only to cracking and rearrangement of the amount of raw material naphtha, which is necessary to maintain the octane number without a strong decrease in volume of the product to the gasoline boiling range.

 The active component of the catalyst, such as zeolite, is usually used in combination with a binder or carrier, since the particle sizes of the behaving as pure zeolite material are too small and lead to an excessive decrease in pressure in the catalytic layer. This binder or carrier, which is preferably used to carry out this step, is a suitable and refractory binder material. Examples of such materials are well known and typically include silica, silica-alumina, silica-zirconia, silica-titania, alumina.

 The catalyst used in this step of the process may not contain any metal component for hydrogenation, or it may include the function of a metal for hydrogenation. If it is found that it is desirable to use specific raw materials under existing conditions, metals such as ordinary Group VIII metals, mainly molybdenum, or combinations thereof are usually used. Noble metals, such as platinum or palladium, do not have an advantage over nickel or other common metals.

Hydrotreating in the second stage
Hydrotreating the effluent of the first stage can be accomplished by contacting the feed with a hydrotreating catalyst. Under hydrotreating conditions, at least some of the sulfur compounds present in naphtha that remain unchanged after the cracking / aromatization step are converted to hydrogen sulfide, which is removed when the desulfurized effluent enters the separator following the hydrotreatment unit. The desulfurized product boils essentially within the same boiling range as the raw material (gas boiling range), but which has a lower sulfur content than the raw material. The sulfur content in the product is typically below 300 mass. ppm and in most cases below 50 mass. ppm The nitrogen content is also reduced to levels typically below 50 mass. ppm, usually below 10 mass. ppm by conversion to ammonia, which is also removed in the separation step.

 If the pre-treatment step is carried out prior to the catalytic treatment in the first step, the same type of hydrotreating catalyst can be used as in the second step of the process, but the conditions can be milder so as to minimize olefin saturation and hydrogen consumption. Since the saturation of the first double bond in dienes is kinetically / thermodynamically favorable relative to the saturation of the second double bond, this goal can be achieved by appropriate selection of conditions. Appropriate combinations of processing parameters, such as temperature, hydrogen pressure and mainly space velocity, can be found empirically. The effluent from the pre-treatment plant can be directly sent to the first stage of the treatment, with hydrogenation reactions proceeding with a slightly exothermic result, providing a useful temperature increase to initiate for the most part endothermic reactions during the processing in the first stage.

In order to preserve the octane number of the product and the volume, the conversion to products boiling below the boiling range of gasoline (C _5- ) is kept to a minimum during the second stage of desulfurization. The temperature of this stage, respectively, is 220-454 ^about C (400-850 ^about F), preferably 260-400 ^about C (500-750 ^about F), and the exact choice depends on the desulfurization required to obtain raw materials, using the selected catalyst . The temperature rise occurs under the exothermic reactions, the magnitudes 11-55 ^{° C (about} 20-100 F) is typical under most conditions and temperature at the inlet to the reactor are preferably in the range 260-400 ^{° C (about} 500-750 F) .

Since cracking naphtha desulfurization is usually easy, low to medium pressures can be used, typically 445-10443 kPa (50-1500 psi), preferably 2170-7000 kPa (300-1000 psi). The pressures represent the total pressure of the system at the inlet to the reactor. The pressure is usually chosen so as to maintain the desired aging rate of the catalyst in use. The volumetric hourly velocity of the liquid (desulfurization step) is typically 0.5-10 (hour ^-1 ), preferably 1-6 (hour ^-1 ). The ratio of hydrogen to hydrocarbon feed is typically 90-900 l / l (under normal conditions) [500-5000 standard cubic feet per barrel], typically 180-445 l / l (under normal conditions) [1000-2500 standard cubic feet per barrel ]. The degree of desulfurization depends on the sulfur content in the feed and, naturally, on standard sulfur standards in the product with appropriately selected reaction parameters. Typically, according to the method, a combination of conditions is used, such that desulphurization should be at least 50%, preferably at least 75%, compared to the sulfur content of the feed.

 The catalyst used in the hydrodesulfurization step corresponds to a traditional desulfurization catalyst, which is a metal of group VI and / or group VIII of the periodic system of elements on an appropriate support. Group VIII metal is usually molybdenum or tungsten, and Group VI metal is usually nickel or cobalt. Their combinations are typical, such as nickel-molybdenum or cobalt-molmoden. Other metals having hydrogenation functionality are also suitable for this step. The catalyst carrier is usually a porous solid, usually alumina, or silica-alumina, but other porous substances, such as magnesium oxide, titanium dioxide, or silica, used either individually or mixed with oxide, can also be used. aluminum or silica-alumina.

 Particle size and the nature of the catalyst are usually determined by the type of conversion process carried out, such as: a liquid phase process with a fixed catalyst bed and a downward stream of feed; liquid-phase method with a fixed catalyst bed and with an upward flow of raw materials; a liquid-phase or gas-phase bubble-type method with a fixed bed of fluidized material; or a liquid-phase or gas-phase method of a transport type with a fluidized bed of catalyst, as described above, moreover, it is preferable to operate as a downward flow of raw materials and a fixed catalyst bed.

Examples
The fraction with the temperature of the boil-off 99 ^{° C} + (210 ^{of the} F +) naphtha fluid catalytic cracking process, the composition and properties of which are presented below in Table 1, are introduced together with hydrogen in a fixed bed reactor the catalyst containing ZSM-5 catalyst having the properties listed below in table 2.

All effluent from the first reactor is sent to the second fixed bed reactor containing a commercial CoMo / Al ₂ O ₃ catalyst (Akzo K742-3Q). The feed rate is constant, such that the hourly space velocity of the liquid through the ZSM-5 catalyst is 1.0 (hour ^-1 ) and the hourly space velocity of the liquid through the hydrotreatment catalyst is 2.0 (hour ^-1 ). The total pressure in the reactor is maintained at 4171 kPa (590 psi) and the simultaneous supply of hydrogen is constant at 356 l / l (under normal conditions) [2000 standard cubic feet per barrel] of naphtha. Reactor temperature with ZSM-5 ranges from 205 ^o C to 427 ^o C (400 to 800 ^° F), while the reactor temperature hydrotreatment (HDT) is 260-370 ^{° C (about} 500-700 F). The results are presented below in table 3.

As can be seen from table 3, an increase in temperature in the case of ZSM-5 at a constant hydrotreatment temperature strictly leads to an increase in octane numbers and a decrease in C ₅₊ yields. You can also achieve degrees of desulfurization above 94%. Hydrogen consumption increases with increasing temperature of ZSM-5 due to the increasing conversion of cracking naphtha olefins when using an acid catalyst rather than in the case of hydrogen-consuming reactions using a hydrotreating catalyst; hydrogen consumption can be further reduced by lowering the hydrotreating temperature to 260 ^{° C.} (500 ^° F.) with a slight hydrodesulfurization effect. This lower hydrotreating temperature also leads to an increase in the octane number of the product, while the saturation of aromatic hydrocarbons decreases. Aromatization of olefins and naphthenes of the feedstock occurs to a low degree and during both stages of the process, the content of aromatic hydrocarbons can even be reduced relative to the feedstock. The yields of liquid products are high in all cases, with the highest yields achieved at low temperatures in the first stage, when product volume increases can be achieved.

Claims (10)

1. A method of improving the quality of the sulfur-containing olefin fraction of raw materials boiling within the boiling range of gasoline, which contains paraffins, including low-octane n-paraffins, olefins and aromatic hydrocarbons, characterized in that the method includes contacting the sulfur-containing cracking under mild conditions in the first stage fractions of the feed at a temperature of 204-427 ^° C, with a solid acid catalyst consisting essentially of ZSM-5 zeolite, having an acid activity with an alpha value of 20-800, for the conversion of olefins present in the feed, into aromatic hydrocarbons and aromatic side chains and for cracking paraffins and olefins in the feed to obtain an intermediate product; contacting the intermediate product with a hydrodesulfurization catalyst at a combination of elevated temperature, elevated pressure and a hydrogen-containing atmosphere to convert sulfur-containing compounds in the intermediate product into inorganic sulfur compounds and obtain, with a yield of at least 90 wt.%, based on the above fraction of a crude, desulfurized product including usually a liquid fraction with a boiling range of gasoline containing less than 50 wt.%. C ₆ -C ₁₀ . 2. The method according to claim 1, characterized in that the aforementioned fraction of naphtha cracking is a light fraction of naphtha with boiling limits in the range from C ₆ to 166 ^o C. 3. The method according to claim 1, characterized in that the above fraction of naphtha cracking is a wide fraction of naphtha with boiling limits in the range from ₅ to 216 ^° C. 4. The method according to claim 1, characterized in that the aforementioned naphtha cracking fraction is a heavy naphtha fraction with a boiling range in the range of 166 to 260 ^° C. 5. The method according to claim 1, characterized in that the aforementioned naphtha cracking fraction is a heavy naphtha fraction with a boiling range in the range of 166 to 211 ^° C.  6. The method according to claim 1, characterized in that the above fraction of naphtha cracking is an olefin fraction of catalytic cracking of naphtha.  7. The method according to claim 1, characterized in that the hydrodesulfurization catalyst contains a metal of group VIII and group VI of the Periodic system of elements.  8. The method according to claim 1, characterized in that hydrodesulfurization is carried out at a pressure of from 379 to 10446 kPa, hourly volumetric flow rate of a liquid of 0.5-10 and a ratio of hydrogen to hydrocarbon feedstock of 89-890 l / l (under normal conditions). 9. The method according to claim 1, characterized in that the hydrodesulfurization is carried out at a temperature of 260-399 ^o C, a pressure of 2172-6998 kPa, hourly space velocity of the liquid 1-6 and the ratio of hydrogen to hydrocarbon feed 178-445 l / l (at normal conditions). 10. A method of improving the quality of the sulfur-containing fraction of the feedstock boiling within the boiling range of gasoline, which contains mononuclear aromatic hydrocarbons and olefins together with low-octane paraffins, characterized in that the first stage of refinement involves the conversion of olefins present in the feedstock into aromatic hydrocarbons and aromatic side chains, cracking of paraffins and olefins in the feed under mild cracking conditions at a temperature of 204-427 ^o C, to obtain an intermediate product by introducing into contact sulfur content your fraction of naphtha with a zeolite catalyst with an average pore size consisting essentially of ZSM-5 zeolite, having an acid activity with an alpha value of 20-800; hydrodesulfurization of the intermediate product in the presence of a hydrodesulfurization catalyst, at a combination of elevated temperature, elevated pressure and hydrogen-containing atmosphere to convert sulfur-containing compounds in the intermediate into inorganic sulfur, to obtain a desulfurized product in which the content of aromatic compounds is not more than 25%, more than in such raw materials, with a total yield of liquid products of at least 90 vol.%, relative to the raw materials.

Images